Acoustic emission (AE) characteristics of surface-to-surface furniture joints connected using adhesive only, staples only, and a combination of adhesive and staples were investigated under lateral load. AE cumulative counts-time curves of the evaluated joints can be divided into three distinct stages based on AE count rates: initiation, growth, and acceleration. The adhesive-stapled joints exhibited two sub-stages (Stage I and II) within the acceleration stage, whereas adhesive-only and stapled-only joints exhibited a single acceleration stage. The AE count rates of stapled-only joints in the initiation and growth stages are higher than the corresponding values for adhesive-only and adhesive-stapled joints. Adhesive-stapled joints exhibited a higher AE count rate than adhesive-only joints and stapled-only joints during the acceleration Stage I. Acceleration Stage II in adhesive-stapled joints has a much lower AE count rate than Stage I. These stage-specific count rate differences reveal distinct AE characteristics of three fastening systems, which have not been previously reported. These findings provide quantitative insights that can inform furniture frame structural design and quality performance testing.

There is an ongoing need to identify high performance materials for use as core material in three-ply industrial mats. To this end, bamboo scrimber and comparably sized red oak planks were tested in bending herein. As raw materials, the bamboo scrimber was procured from market stock that is currently used commercially as flooring. The red oak was sawn from planking used for three-ply mat construction. Respectively, the design strength and stiffness of the bamboo scrimber planks were 45% and 28% greater than the red oak. Based on T-tests, these differences were statistically significant at the alpha 1/4 0.05 level. These findings suggest that bamboo scrimber planking may be a candidate for use as core material in three-ply matting in cases where oak or other domestic wood species are not available.

Four mechanical models were proposed to derive formulas predicting the bending moment capacities of layered particleboard under simply supported center-loading. Experimental validation confirmed these models are effective tools for describing the bending moment development process, including proportional limit, yield, and ultimate points. With predicted and experimental ratios ranging from 0.88 to 1.04, Model 4 can reasonably predict the ultimate bending moment capacity of elastic–plastic and bi-modular-layered particleboard materials. Photo-elastic testing revealed neutral axis shifting toward the compressive side, resulting from the face layer’s significantly higher mean modulus of elasticity in compression than in tension. Additionally, the core material above the centerline of PB thickness contributed to tensile resistance. The proposed mechanical models require inputs such as the tensile and compressive strengths and thickness of each layer, accounting for the asymmetric strength profile and neutral axis shifting. The main conclusion was that the bending moment resistance of the particleboard depends on the combined effect of tensile and compressive strengths of all layers. A 3D plot visualized the PB’s mechanical design space, displaying feasible tensile–compressive strength combinations of particleboard layers. This enables determination of optimal strength properties for each layer. For M2 grade particleboard, the most cost-effective design occurred when the face layer reached a 5.38 MPa tensile strength, with the compressive strength ranging between 13.00 and 18.59 MPa.

Glued-laminated timber (Glulam), a structural engineered wood product, is mostly manufactured using structural adhesives including one-component polyurethane (PUR). Nevertheless, the concerns associated with PUR such as unsatisfactory gap-filling properties and lower resistance to delamination create opportunities for newer adhesives with enhanced bonding performance in outdoor environments. In this study, the use of fractionated lignin as a modifier in a polyurethane-based adhesive system was explored. Herein, the effect of lignin content (1, 2, and 3%) on the block shear strength (BSS), wood failure percentage (WFP), and delamination were evaluated. The results indicated that all the lignin-reinforced PUR specimens showed better adhesion performance compared to the controls (without lignin). Markedly, the lignin-PUR adhesive formulation containing 1% lignin addition exhibited superior adhesion properties than those with 2% and 3% lignin content. The statistical analyses also revealed that the lignin content influenced the BSS and WFP of the glulam specimens. Moreover, the lignin-modified PUR specimens showed increased delamination resistance and met the requirements for delamination stipulated in the ASTM D2559 standard, regardless of the lignin content. The lowest percent delamination (0.07%) was obtained from specimens bonded with 1% lignin. The presented data suggest that specimens bonded with 1% of lignin provided better bonding strength compared to other lignin-filled specimens. Thus, this study demonstrated the technical feasibility of fabricating glulam with enhanced adhesion performance using lignin-modified PUR adhesive.

This study investigated the influence of wood grain angle (0 degrees, 10 degrees, 20 degrees, 30 degrees, 45 degrees, 60 degrees, 75 degrees, and 90 degrees) on acoustic emission (AE) characteristics of southern yellow pine columns subjected to compressive loading. Four AE parameters considered were counts, cumulative counts, count rate, and amplitude. The main conclusion was that AE cumulative counts vs time curves can be characterized by three distinct stages in terms of AE count rates: initiation, growth, and acceleration. The initiation stage had a constant mean count rate of 0.33 counts/s compared with the growth stage mean count rate of 19.10 counts/s, whereas the acceleration stage had a mean count rate of 608.40 counts/s. Within each stage, count rates increased as the grain angle increased from 0 degrees to 30 degrees, then dropped as the grain angle further increased to 90 degrees. Maximum AE counts and total cumulative AE counts all increased as the grain angle increased from 0 degrees to 30 degrees and decreased as the grain angle further increased to 90 degrees. Higher AE amplitudes were observed in the yield and failing stages of tested wood columns according to their stress-strain curves plotted together with their corresponding amplitude-time curves. Maximum amplitude increased as the grain angle increased from 0 degrees to 20 degrees, then had a decreasing trend as the grain angle increased to 45 degrees, followed by an increasing trend as the grain angle increased to 75 degrees. These differences in AE characteristics suggested that AE "signatures" in terms of AE signals do exist for timber materials when subjected to compressive loading.

To expand the use of cross-laminated timber (CLT) to exterior applications, there is a need to protect the panels from biodegrading agents such as fungi and termites. Pressure treatments are effective methods of increasing the durability of wood and wood-based products; however, studies on pressure-treated CLT are limited. In this study, preservative-treated CLT samples from prefabricated CLT panels were prepared and impregnated with Cu-based preservatives through a conventional vacuumpressure process. The effects of panel layup (3-ply parallel, 3-ply perpendicular, and 5-ply parallel) and preservative treatment (untreated [control], copper azole-type C [CA-C], and micronized copper azole-type [MCA]) on the bonding performance were investigated. Panel layup and preservative treatment had a significant influence on the block shear strength and percentage of wood failure (WFP) of the treated panels. Overall, approximately 60 percent of the block shear specimens had a WFP of >75 percent. However, fewer than 10 percent of the delamination specimens met the ASTM D2559 (2018) limitation of 1 percent for softwood used in outdoor applications. ASTM D2559 counts shallow wood failure as delamination, which could have been a reason for the high delamination rate. The percentage of wood failure and the high rate of delamination could be due to the moisture-induced adhesion failure resulting from the pressure-treatment process. The preservative pressure-treatment of the CLT panels increased the moisture content (MC) from 12-15 percent to approximately 85 percent MC, and the severe swelling of the panels during treatment might have imposed a high stress on the bond line. However, no noticeable delamination of the panels was observed during the actual treating phase of the study. These results show the feasibility of treating prefabricated CLT panels with CA-C and MCA preservatives without compromising the bonding strength.

Cross-laminated timber (CLT), a prefabricated multilayer engineered wood product, is a promising construction material for mid-and-high rise buildings due to its good mechanical properties, renewability, and low-carbon footprint. However, the vulnerability of CLT to biodeterioration limits its broad applications. Preservative treatment is an effective method of increasing the service life of structural wood products, while the treatment of CLT has not been widely studied. Herein, we fabricated 3- and 5-ply CLT panels and treated them with Cu-based preservatives. The effects of panel layup (lengthwise and crosswise) and thickness (3-and 5-layer) on the impregnation quality (i.e., Cu penetration and retention) are investigated using a color-based indicator approach and X-ray fluorescence spectroscopy . Generally, the Cu penetration ratio was mostly above 90%, especially for the top layers (1st layer in 3-ply and 1st and 2nd layers in 5-ply) of the treated CLT panels. Similarly, higher Cu retention values were observed in the 1st layer of the 3- and 5-layer CLT panels. Further, there was a similarity in the Cu penetration of the 2nd layer in 3- and 5-ply CLT, indicating the preservative diffusion across adjacent layers is negligible in the preservative treatment of lumber-based wood composites. Overall, copper-azole type C (CA-C) exhibited better treatability than micronized copper azole (MCA) for CLT panels, resulting in higher Cu penetration and retention across the panels. Also, we found the lengthwise orientation preferable in fabricating preservative-treated CLT, this is due to the complete panel protection of the 1st and 2nd layers at all panel locations. Thus, our results show the feasibility of successfully treating CLT, especially when CA-C preservative and lengthwise orientation are utilized in fabricating the panels.

This study investigated the influence of growth rings (earlywood, earlywood and latewood interface, and latewood) on the mode I fracture toughness of solid wood of the two species southern yellow pine (Pinus taeda L.) and red oak (Quercus falcata) subjected to cracking loads in their radial-longitudinal crack propagation system. Experimental results indicated that southern yellow pine latewood had a significantly greater fracture toughness than its earlywood as well as its earlywood and latewood interface. The earlywood and latewood interface of southern yellow pine had a greater fracture toughness than its earlywood, but this difference was not significant. Red oak latewood had a greater fracture toughness than its earlywood and latewood interface, however this difference was not significant. Red oak earlywood had a significantly lower fracture toughness than its latewood and earlywood and latewood interface. In general, red oak had a significantly greater fracture toughness than southern yellow pine. The differences in specific gravity among latewood, earlywood and latewood interface, and earlywood for each of the two wood species evaluated were significant. The mode I fracture toughness of a tested wood block in its radial-longitudinal crack propagation system can be affected by not only its specific gravity but also by its microstructure such as ray cell size and quantity. The regression analyses indicated a strong positive linear relationship existed between the fracture toughness and specific gravity for the two wood species evaluated. The rate of increase in fracture toughness of red oak was about three times of southern yellow pine as their specific gravity increased.

There is a pressing need to develop engineering standards for timber- and other wood-based mats suitable for supporting construction vehicles, etc. In 2018, a group of mat producers and users began discussing a potential grading standard specific to mats. There are large gaps in the literature regarding the performance of the available raw materials as well as bolt-laminated mat systems. This study addresses the issue of determining the strength and stiffness values of a commercially sourced industrial bamboo mat. A total of seven 8 ft × 14 ft (2.44 m × 4.27 m) commercial bamboo mats were cut into 28 billets that were 21.5 in (54.6 cm) in width. The bamboo mat billets were evaluated for bending stiffness (modulus of elasticity [MOE]) and strength (modulus of rupture [MOR]) using a three-point static bending test. The 5th percentile non-parametric tolerance limit (5% NTL) and design value for fiber stress in bending (Fb) were calculated. The mechanical property values measured for the 3-ply bamboo mat were at least 25% less than values reported for mixed hardwood timber mats. This type of structural performance information is helpful and useful in the development of matting standards, as it describes the minimum performance characteristics for this type of composite matting.

In this research, flexural properties of mill-run, in-grade red and white oak lumber from a single mill and commercially available laminated hardwood composite were evaluated. Structurally graded green (wet) freshly sawn red and white oak 5 by 10-cm (2 by 4-in) nominal lumber as well as glue-laminated hardwood composite billets were tested in bending and their modulus of rupture (MOR) and modulus of elasticity (MOE) properties were developed. It is well documented that MOR and MOE are two major indicators to evaluate flexural strength of wood lumbers. From these data, summary statistics, design values, and mean separations were calculated and reported. Overall, the red and white oak lumber performed similarly to structural No. 2 grade material. The hardwood composite billets were highly uniform. Each of the three materials demonstrated a reasonably good relationship between MOE and MOR, thereby suggesting that MOE could be used as a selection criterion for strength in a commercial use situation.

Sitting comfort is primarily determined by the cushioning capability of the seat foundation. Limited literature has been found related to the effects that different sized human buttocks had on the cushioning capability of the seat foundation. Moreover, there is no testing method specialized to measure the load-deformation behavior of foam cushions that imitates the sitting behavior between indenters with different sizes and seat support. This study investigated the effects of various indenter diameters (20 cm, 30 cm, 36 cm, 41 cm, 51 cm, and 58 cm), foam stiffness levels (high and low), and seat bases (spring versus solid flat panel) on the compressive load-deformation behavior of upholstered seat foundations. The load-deformation curves of all the tested foam-seat base combinations exhibited three typical regions, i.e., linear elasticity, plateau, and densification, when subjected to the loads applied through different indenter diameters. Statistical results indicated that the primary effects of the indenter diameter, foam stiffness level, and seat base had significant effects on the spring constants, which represented the slopes of lines in these three regions. In addition, a regression technique was proposed to derive power equations for the estimation of the spring constants of a seat foundation as a function of the indenter diameter, foam material stiffness, and seat base type.

The effect of the end distance was studied relative to the static ultimate lateral load capacity of a single-shear unconstrained wood-plasticcomposite-to-metal single-bolt connection (SUWSC). Equations estimated the static ultimate lateral loads of the SUWSCs that failed during the end tear-out, splitting, and yield modes and were obtained using stress concentration factor regression- and mechanics-based approaches. The experimental results showed that the stress concentration factor was a linear function of the end-distance to bolt-diameter ratio for the SUWSCs that failed during end tear-out and splitting modes. The static ultimate lateral loads of the SUWSCs that failed during the yield modes were estimated using a mechanics-based equation. The minimum end distance for the SUWSCs that failed without end fracture (i.e., only with yield mode) was 25.4 mm, which was four times larger than the bolt diameter.

The wood dowel pin is one of the common fasteners for connecting structural members in wooden furniture frame construction, such as chairs. The effects of dowel penetration depth, shear strengths of connection member and dowel materials, dowel surface texture, and member grain orientation on ultimate direct withdrawal loads of single dowels withdrawn from wooden materials were investigated. The main findings were that the connections using dowels and main members with low shear strength properties achieved the same ultimate direct withdrawal loads with connections using the materials with higher shear strength properties for dowels and main members. Additionally, the existing empirical equations, including shear strength properties for both dowel and main member materials used to construct dowel connections, tended to remarkably underestimate the ultimate direct withdrawal loads of the evaluated dowel connections withdrawn from the end and side grains of the tested wood species. The connection main members in this study when these two shear strength values were added together was less than 25 MPa. Both estimation expressions were modified to consider the lower shear strength effort on ultimate direct withdrawal loads of dowels evaluated in this experiment.

Characteristics of torques for driving screws into particleboards were investigated in this study. Factors evaluated on screw seating and stripping torques (SET and STT) were pilot-hole diameter, embedded screw orientation, and particleboard (PB) material physical and mechanical properties such as material core density, particle size, and internal bond (IB) strength. Recorded torque time curves, which illustrate the complete process of driving screws into PB materials, indicated that screw torques behave similarly in sides and faces of PB and that the whole screwdriving process can be described as a two-phase process. PB materials evaluated in this study had mean SET from 0.66 to 1.94 N-m, STT from 2.03 to 6.51 N-m, and SIT-to-SET ratios from 2.5 to 5.0. Statistical analyses indicated that the SET and STT of driving screws into PB faces were significantly greater than their corresponding values into PB edges. The SET and STT in PB materials with pilot holes were lower than their corresponding ones without pilot holes. SET and SIT values can be estimated using power equations including PB material core density and particle length and IB strength.

This study investigated the lateral shear and tensile load resistances of glued face-to-face and end-to-face joints in southern yellow pine plywood and oriented strandboard (OSB). Face-to-face joint test results indicated that glued plywood joints had more resistances to shear and tensile loads than OSB joints, and tested joints constructed in both the plywood and OSB showed significantly higher lateral shear load resistance than tensile load resistance. The face grain orientation of joint members had a significant effect on the load resistances of plywood joints, but not on OSB joints. End-to-face joint strength evaluation showed that tested joints had significantly higher lateral shear load resistance than tensile load resistance, and the resistances of plywood joints to shear and tension loads were statistically higher than those of OSB joints. The wax on OSB surfaces tended to weaken joint load resistances.

Squeaking and creaking noise from selected components of two stationary three-seat bare sofa frames, one with glue applied to joints and the other one with no glue applied, were evaluated by subjecting them to the General Services Administration performance tests. The main purpose of this evaluation was to compare frame construction performance differences between the construction of joints with glue and without glue as it relates to the onset of squeaking. An acoustic emission apparatus utilizing microphones as noise detection sensors was used to detect the noise signals. Experimental results of recorded squeaking signal in terms of loading cycles completed until the first audible squeak indicated that, in general, the joints with no glue started squeaking earlier than the ones with glue applied, but their squeaking occurred at the same load level. The General Services Administration performance test standards define frame failures as frames suffering disability to resist testing loads applied on the frames. A frame strength performance rating is given to a tested frame based on the load level of which it passed. There was no difference in fatigue performance between glued and unglued frames. But, results of our acoustic emission study revealed that, in general, the load level corresponding to first squeak occurring was one to two load levels lower than the load level passed by a frame tested before it failed from broken components.

This study investigated fatigue performances of T-shaped, end-to-side, metal-plate-connected (MPC) joints in furniture-grade pine plywood. Tested joints were subjected to one-sided cyclic stepped bending loads. The purpose of the study was to obtain Joint static to fatigue moment capacity ratios. Performance test results showed that a MPC plywood joint would fail within 25,000 cycles when a stepped load level reached 46 percent of the static moment capacity of the tested joint. Joints failed mainly due to tooth fatigue shear at the roots. The static to fatigue moment capacity ratio for tested joints averaged 2.5 with a coefficient of variation of I I percent and a range of 2.2 to 3.1.

Effects of in eta I plate length and width, and joint rail width on the moment capacity of the T-shaped, end-to-side, metal-plate-connected (M PC) joints in furniture grade, 3/4-inch-thick 7-ply southern yellow pine plywood were investigated. Experimental results indicated that metal-plate and rail widths affected the moment capacity of MPC plywood joints significantly. Moment capacity increased significantly as metal-plate lengths increased from 3 to 4.5 inches, but no significant moment increase occurred as metal-plate lengths increased from 4.5 to 7.5 inches with an increment of 1.5 inches. The average moment capacity of tested joints in this study ranged from 2,863 to 13,721 lb.-in. The minimum metal-plate length to prevent having joints with tooth withdrawal failure and to have joints fail with plate yield mode is 6 inches. The moment capacity of MPC joints in pine plywood can be reasonably estimated with existing mechanics based models.

Edge lateral resistances of T-shaped, face-to-edge single- and multi-staple joints in furniture-grade, 3/4-inch-thick 5-ply southern yellow pine plywood were investigated. Experimental results indicated that staple penetration depth and the number of staples positively affected the edge lateral resistance of staple joints in the pine plywood. Tested joints tended to show higher lateral resistances when they were subjected to loads perpendicular to the fastening member thickness direction, compared to when they were subjected to parallel loads. Single-staple joint experimental results indicated that staple crown orientation effect on edge lateral resistance became significant when staple penetration depth increased to I inch and deeper, and that ply-grain orientation had no significant effect on lateral resistance. Multi-staple joint tests showed that plywood internal bond strength could be the major limiting factor for the lateral resistance of the multi-staple joints in the pine plywood when they are subjected to loads parallel to the fastening member thickness direction. Regression analysis results indicated that a non-linear relationship existed between lateral resistance and staple penetration depth for the joints evaluated in this study. The power multiple regression equation quantifies the effects of significant factors on the average edge lateral resistance of T-shaped, face-to-edge staple joints in the 5-ply pine plywood.